High/low aspect ratio dual-mode fin design

ABSTRACT

A dual-mode fin design for gun-launched, rocket-assisted, guided projectiles in which, from a flush position against the body, the fins rotate radially at launch to deploy in the low aspect-ratio mode for stability during the supersonic fly-out phase with transition to the high aspect-ratio mode for the transonic termianl maneuvering phase. Deployment of the fins to high aspect-ratio mode is effected by shearing restraining pins which allow the fins to rotate rearwardly about pivot pins and under the air stream influence.

Hones Feb. 5, 11974 [54] g gg gg ig RATIO DUAL-MODE FOREIGN PATENTS on APPLICATIONS 325,802 7/1970 Sweden 244/327 [75] Inventor: Daniel A. Jones, Fredericksburg, 1,118,055 11/1961 Germany 244/328 Va. 1,199,664 7 8/1965 Germany 244/3 29 [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: Mar. 12, 1973 [21] Appl. No.: 340,123

[52] US. Cl 244/327, 244/328, 244/329 [51] Int. Cl. F421) 13/32 [58] Field of Search 244/3.27-3.29

[56] References ited UNITED STATES PATENTS 3,515,360 6/1970 Alexander 244/328 3,643,599 2/1972 Hubich 244/327 Primary ExaminerVerlin R. Pendegrass STRACT A dual-mode fin design for gun-launched, rocketassisted, guided projectiles in which, from a flush position against the body, the fins rotate radially at launch to deploy in the low aspect-ratio mode for stability during the supersonic fly-out phase with transititmt e, g p tmoiz etlhentrans n terminal maneuvering phase. Deployment of the fins to high aspect-ratio mode is effected by shearing restraining pins which allow the fins to rotate rearwardly about pivot pins and under the air stream influence.

5 Claims, 2 Drawing Figures HIGH/LOW ASPECT RATIO DUAL-MODE FIN DESIGN BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to guided projectiles and more particularly to a dual-mode fin design to satisfy conflicting aerodynamic design requirements for a full-bore, gun-fired, rocket-assisted, terminally-guided projectile.

2. Description of the Prior Art In the past, designers of guided projectiles experiencing various Mach regimes of flight have been forced to compromise in the fin design between low aspect-ratio fins and high aspect-ratio fins. Low aspect-ratio fins provide minimum drag during the supersonic fly-out phase, but yield low lift during the transonic terminal guidance phase. On the other hand, high aspect-ratio fins provide high lift during the transonic terminal guidance phase, but impose a high drag penalty during the supersonic fly-out phase.

The requirements for a full-bore, rocket-assisted projectile limit the possibilties for fin designs to those that (1) do not extend beyond the body outer diameter in the stowed position and (2) do not significantly reduce the volume available for a rocket motor. This would seem to eliminate consideration of high aspect-ratio trailing fins which rotate forward for deployment. Further, high aspect-ratio fins which lie along the body and deploy radially and rearwardly through a cammed double-hinge arrangement appear to be unacceptable because of the large drag penalty arising from the required fin thickness for launch structural integrity together with the aspect-ratio factor at supersonic speeds. Similar considerations seem to apply even if the double hinge is replaced by a single slant-axis hinge such as that illustrated in U.S. Pat. Nos. 3,127,838 and 3,602,459.

On the other hand, low aspect-ratio fins which stow along the body and rotate radially for deployment, such as those illustrated in U.S. Pat. No. 2,858,765, may be designed for launch structural integrity without incurring a large drag penalty, but these fins cannot provide deployment maneuver capability for terminal guidance which occurs at transonic speeds due to the low lift factor.

SUMMARY OF THE INVENTION Terminally guided projectiles are customarily steered or guided by the operation of a guidance system on canards which are deployed from the forward portion of the projectile during the transonic terminal guidance phase together with rear mounted fins which provide lift surfaces. Ideally, the fins should be of low aspectratio to achieve fin structural integrity at launch and provide stability with a minimum drag penalty during the supersonic fly-out phase and of high aspect-ratio for maximum maneuvering capability during the transonic terminal guidance phase. The present invention combines the best aerodynamic features of both low and high aspect-ratio fins without the disadvantages of each by providing fins which rotate radially into a low aspect-ratio position upon launch and then rotate rearwardly into a high aspect-ratio position at the time the canards are deployed during the terminal guidance phase at transonic speeds. Since transition to the high aspect-ratio mode prior to the start of terminal guidance occurs in a portion of the flight regime where the air stream dynamic pressure is relatively low, structural integrity is easily achieved relative to the previously discussed cases of deploying high aspect-ratio fins at launch with the attendant high dynamic pressure. A further advantage of the dual-mode fins is that the fins may be canted in the low aspect-ratio mode to roll the projectile above the resonant frequency at a rate optimum for averaging thrust and configurational asymmetries during the supersonic fly-out and the cant removed during the transition to the high aspect-ratio mode by inclining the pivot pin axis thus achieving the desired slow roll rate, i.e. below resonance, for terminal guidance.

STATEMENT OF THE OBJECTS OF THE INVENTION It is a primary object of this invention to provide a new and useful fin design for gun-launched guided projectiles.

It is another object of this invention to provide a fin design for guided projectiles capable of functioning in both low and high aspect-ratio modes.

It is a further object of this invention to provide a fin design for gun-launched guided projectiles which function in a low aspect ratio mode during supersonic flyout and a high aspect-ratio mode during transonic terminal guidance.

It is yet another object of the invention to provide a high/low aspect-ratio dual mode fin design embodying launch structural integrity for a rocket-assisted projectile which does not significantly reduce the volume available for the rocket motor.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and novel features of the invention will become readily apparent upon consideration of the following detailed description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a side view, partially in section, of a fullbore, gun-launched, rocket-assisted, terminally-guided projectile embodying the principal features of the invention and illustrating both the low and high aspectratio modes of the projectile fins; and

FIG. 2 is a rear view of the projectile of FIG. ll illustrating the pre-launch stowed position of the fins.

DESCRIPTION OF THE PREFERRED EMBODIMENT Attention now is directed to the drawings, and more particularly to FIG. ll wherein is disclosed a projectile generally designated by the reference numeral 10 and comprising an ogive section ill, a full-bore section 12, and a rearward section 14 of reduced diameter. A plurality of fin bases 15 are circumferentially spaced about the section 14 and are normally held thereon by means of shear pins 16 and pivot pins 18. A plurality of fins 19 are pivotally mounted on the fin bases 15 by means of hinge pins 20 (FIG. 2). As can be seen from FIGS. 1 and 2, the rearward section 14 is of substantial diameter relative to the full-bore section 12 and thus is suitable for accommodation of a rocket-motor to provide a rocket-assisted projectile. The rocket motor has been omitted from the drawings because specific rocket motor details are not germane to the construction or the operation of the present invention.

A shearing device 21 is disposed within the rearward section 14 adjacent the shearpins 16. The shearing device 21 may be of any suitable or appropriate construction, tag. a cartridge actuated or explosive device. The full-bore section 12 also accommodates a guidance system 22. The guidance system may likewise be of any appropriate design since the functioning of the present invention is not dependant upon any specific construction or mode of operation of the guidance device.

OPERATION In order that a better understanding of the invention might be had, its mode of operation will now be described. Prior to gun launch, the fins 19 will all be in the stowed position illustrated in the left-hand portion of FIG. 2. When the projectile exits from the gun tube (not shown) it will possess a roll-rate of approximately -15 cps due to the gun tube rifiing. Due to this rollrate, the fins 19 will rotate about the hinge pins in the direction of the arrow in FIG. 2 and assume the low aspect-ratio mode position designated generally by the reference numeral 24. The shear pins 16 and pivot pins 18 may be displaced circumferentially relative to each other to cause the fins 19 to assume canted positions relative to the longitudinal axis of the projectile to assure maintenance of a roll-rate above the resonant frequency during the supersonic fly-out phase as previously described.

At the appropriate point in the trajectory of the projectile 10, the guidance system 22 will actuate the shearing device 21 to shear the pins 16 and free the forward ends of the fin bases 15. The timing of this action may, for example, be determined by a timing device forming a part of the guidance system 22 and initiated by the set-back forces of launch. At about the same time the guidance system 22 will deploy canards (not shown) from the ogive section 11 or full-bore section 12.

When the pins 16 have been sheared, the fin bases 15 and fins 19 will be free to rotate rearwardly in the direction indicated by the arrow in FIG. 1 about the pivot pins 18 to assume the high aspect-ratio mode position designated generally by the reference numeral 25. This pivotal motion will be effected by dynamic pressure, but may be assisted by springs (not shown) if desired. The axes of the pivot pins 18 may be inclined to remove entirely or reduce the fin cant angle to achieve a lower roll-rate below the resonant frequency to facilitate terminal guidance.

From the foregoing it will be readily apparent that Applicant has provided a fin design for guided projectiles embodying numerous advantageous features not found in prior art devices. The present invention provides both high and low aspect ratio fin configurations during different portions of the flight regime as well as facilitating varying roll rates at different portions of the flight regime.

It is to be understood that the invention may be practiced other than as specifically described. Obviously,

many modifications and variations of the present invention will readily occur to those skilled in the art in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A dual-mode fin system for a guided projectile comprising:

a base for mounting said fin on the projectile body;

means connecting said fin to said base for enabling said fin to deploy to a low aspect-ratio mode position; and

means for connecting said base to the projectile body for enabling said fin and base to deploy to a high aspect-ratio mode position.

2. A dual-mode fin system as defined in claim 1 wherein said means connecting said fin to said base comprises a hinge pin which permits pivotal movement of said fin outward from a stored position adjacent the projectile to the low aspect-ratio position.

3. A dual-mode fin system as defined in claim 1 wherein said means for connecting said base to the projectile body comprises a pivot pin which permits pivotal movement of said base and said fin outward from the low aspect-ratio position to the high aspect-ratio position.

. 4. A dual-mode fin system as defined in claim 3 wherein said means for connecting said base to the projectile body includes:

a shear pin which cooperates with said pivot pins to initially hold said base to the projectile body; and

means for shearing said shear pin to enable pivotal movement of said base and said fin about the pivot pm. 5. A dual-mode fin system for guided projectiles comprising:

a fin; a base for mounting said fin on the projectile body;

a hinge pin connecting said fin to said base which permits pivotal movement of said fin outward from a stored position adjacent the projectile body to the low aspect-ratio mode position;

a pivot pin for connecting the rearward end of said base to the projectile body;

a shear pin for connecting the forward end of said base to the projectile body and substantially longitudinally thereof; and

means responsive to a command from the projectile guidance system for shearing said shear pin whereby said base and said fin are free to pivot about said pivot pin under airstream influence from the low aspect-ratio position to the high aspectratio position. 

1. A dual-mode fin system for a guided projectile comprising: a fin; a base for mounting said fin on the projectile body; means connecting said fin to said base for enabling said fin to deploy to a low aspect-ratio mode position; and means for connecting said base to the projectile body for enabling said fin and base to deploy to a high aspect-ratio mode position.
 2. A dual-mode fin system as defined in claim 1 wherein said means connecting said fin to said base comprises a hinge pin which permits pivotal movement of said fin outward from a stored position adjacent the projectile to the low aspect-ratio position.
 3. A dual-mode fin system as defined in claim 1 wherein said means for connecting said base to the projectile body comprises a pivot pin which permits pivotal movement of said base and said fin outward from the low aspect-ratio position to the high aspect-ratio position.
 4. A dual-mode fin system as defined in claim 3 wherein said means for connecting said base to the projectile body includes: a shear pin which cooperates with said pivot pins to initially hold said base to the projectile body; and means for shearing said shear pin to enable pivotal movement of said base and said fin about the pivot pin.
 5. A dual-mode fin system for guided projectiles comprising: a fin; a base for mounting said fin on the projectile body; a hinge pin connecting said fin to said base which permits pivotal movement of said fin outward from a stored position adjacent the projectile body to the low aspect-ratio mode position; a pivot pin for connecting the rearward end of said base to the projectile body; a shear pin for connecting the forward end of said base to the projectile body and substantially longitudinally thereof; and means responsive to a command from the projectile guidance system for shearing said shear pin whereby said base and said fin are free to pivot about said pivot pin under airstream influence from the low aspect-ratio position to the high aspect-ratio position. 